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Cycle coolant out of thermos before working on fluid control valve?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Feb 1, 2022.

  1. pasadena_commut

    pasadena_commut Senior Member

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    Before replacing the fluid control valve (P1121 part) in a coolant system which has not been drained I would like to get the hot coolant out of the thermos bottle. In theory all the hoses will be plugged as they come off and nothing much should leak, but, well, stuff happens. The car will have cooled overnight, so the only hot coolant will be in the thermos. The thing I don't know is how long it would take to pump most of that hot coolant out. So while the "shorting two pins on the control relay" trick could be used to run the relevant pump, I have no idea how many seconds (or bursts of 20s) would be needed to get most of it out. To be clear, here "out" means moved around within the cooling system, not drained into a bucket. Would just starting the car and running the motor for 30s (60s?) do the trick? If I understand it correctly the start up sequence moves the hot coolant out of the thermos first thing. So if the car then sits another 30 minutes off the coolant can cool off quickly in the motor/pipes, rather than staying hot in the thermos bottle. Most of what would be in the bottle at that point would be cold coolant originally from other parts of the cooling system.
     
    #1 pasadena_commut, Feb 1, 2022
  2. JC91006

    JC91006 Senior Member

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    I can't remember the last time I did this, but I'm fairly certain the drain plug was right next to the thermos. I don't think it drains the radiator, drains the thermos
     
    #2 JC91006, Feb 1, 2022
  3. pasadena_commut

    pasadena_commut Senior Member

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    I'm not trying to drain it, just to move the hot coolant in the thermos out to other parts of the cooling system so that it too can cool off.
     
    #3 pasadena_commut, Feb 2, 2022
  4. JahT

    JahT Member

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    I just did this and I think I found the best method to replace the valve based on all of the videos. You don't have to take the headlight off or bumper or anything major, I didn't even jack up the car. Remove the small undercarriage shield from below the thermos tank, you'll see a Tee with hoses under it and a drain petcock. I used that drain to drain the thermos but it essentially drained the entire system of about 1.5 gallons, and if you leave the radiator cap on it will pull the old coolant out of the overflow tank too. Then when you pull hoses on the valve, you'll pull off the top two, but leave the bottom hose attached to valve, and remove the bottom hose's other end from the thermos tank Tee, it is the hose coming into Tee from passenger side direction.

    You will need to pull the bolts off the inverter brackets and wedge something under it to lift slightly as seen in the videos. Then once the two bolts are off of the valve you'll be able to rotate down in that space. The trick I didn't see posted anywhere is to remove the bracket off of the plastic valve body with 3 Philips screws. Then the bracket and valve come out separately and easily. Then remove the bracket from the new valve too to get it down into its space and reattach the bracket in there. Made it so much easier. Then reuse or add new coolant and bleed.
     
    #4 JahT, Feb 3, 2022
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